Motorunits

A motor unit consists of a motor neuron, and all the muscle fibers it controls. The motor neuron cell body is located in the grey area of the spinal column. The individual axon will branch out to all of the muscle cells controlled by that motor neuron. The neuromuscular junction is the connection site of the axon to the muscle cell. Each muscle cell has its own neuromuscular junction. A single motor neuron can control any where from one to hundreds of muscle fibers (Baechle, 5). The movement of a muscle depends on the number of muscle fibers controlled by each motor unit. The quadriceps muscle group has little precision due to low motor neuron to muscle fiber ratio. The muscles of the eye however may have as little as one neuron for each muscle fiber and this is how we can make the precise movements of the eye (Baechle, 5).

led action potential that flows in the motor neuron is not capable of directly contracting the muscle fibers to power. The action potential signals the release of acetylcholine. Once the acetylcholine crosses the neuromuscular junction, another action potential is created to activate the muscle contraction (Baechle, 16).

During this project I learned a lot about motor units and how the body functions. I thought I would hate doing this project, but it seemed to go faster than originally thought. This is definitely one of the best assignments I have had this year.

Each action potential activates the muscle very slightly. This is called a twitch. The first twitch activates the release of acetylcholine releasing calcium causing a small twitch. The second twitch can use the force of the first to create a very strong contraction. Decreasing the time interval between the two twitches results in a greater more forceful contraction. If the twitches are delivered at such a high frequency that they fuse this is called tetanus. Tetanus is the maximum amount of force a motor unit can develop (Baechle, 16).

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